Her-2/neu (referred to henceforth as “Her-2”) is a 185 kDa glycoprotein that is a member of the epidermal growth factor receptor (EGFR) family of tyrosine kinases, and consists of an extracellular domain, a transmembrane domain, and an intracellular domain which is known to be involved in cellular signaling (Bargmann C I et al, Nature 319: 226, 1986; King C R et al, Science 229: 974, 1985). It is overexpressed in 25 to 40% of all breast cancers and is also overexpressed in many cancers of the ovaries, lung, pancreas, and gastrointestinal tract. The overexpression of Her-2 is associated with uncontrolled cell growth and signaling, both of which contribute to the development of tumors. Patients with cancers that overexpress Her-2 exhibit tolerance even with detectable humoral, CD8+ T cell, and CD4+ T cell responses directed against Her-2.
Listeria monocytogenes is an intracellular pathogen that primarily infects antigen presenting cells and has adapted for life in the cytoplasm of these cells. Host cells, such as macrophages, actively phagocytose L. monocytogenes and the majority of the bacteria are degraded in the phagolysosome. Some of the bacteria escape into the host cytosol by perforating the phagosomal membrane through the action of a hemolysin, listeriolysin O (LLO). Once in the cytosol, L. monocytogenes can polymerize the host actin and pass directly from cell to cell further evading the host immune system and resulting in a negligible antibody response to L. monocytogenes. 